This invention concerns a clamping device for clamping work pieces, used in particular in the automotive field for clamping and/or centring metal sheets in the manufacture of motor vehicles, or for other similar uses.
For the purposes of this description, the wording xe2x80x9cclamping devicexe2x80x9d is intended to indicate any toggle-lever gripping device having one or more clamping arms, or one or more hook-shaped members, or a device for retaining a work piece in a centred condition, while the wording xe2x80x9cclamping memberxe2x80x9d is intended to indicate a clamping arm, or a hook-shaped member, or a member for retaining and centring work pieces, which are movable between first and second operative positions.
In general, the toggle-lever clamping devices are known and normally used for clamping work pieces on a supporting structure or against a shoulder surface.
A clamping device of the aforementioned kind, comprises a box-shaped body and a linear actuator of pneumatic, electrical or different type, onto which at least one clamping arm is pivoted to perform an angular movement between an open position and a clamping position to block a work piece against a shoulder or a supporting structure.
The clamping arm is connected to the rod of the actuator, by a toggle-lever mechanism comprising an intermediate connecting link which is hinged to a crank lever of the clamping arm, respectively to the rod of the actuator.
Devices of this kind are known for example from EP 0 803 331 and EP 0 406 530.
In devices of this kind, the clamping arm is made automatically to rotate upon opening and closing, by the same actuator.
For certain applications, or under particular conditions of use, it may be necessary for an operator to manually operate the clamping device, by acting on an appropriate control lever.
For example, DE 299 20 639 describes a clamping device of the aforementioned type, comprising a manual control lever pivotally supported to the box-shaped body of the device, in which the control lever is operatively connected to the clamping arm by a link or control rod.
In particular, the operative connection between the control lever and the clamping arm is achieved by intermediate connecting means comprising an L-shaped lever having one end connected to the rotational axis of the control lever, while the other end of the L-shaped is in the form of a fork member provided with guide rolls sliding along respective guide slots on both sides of a thrust member.
When operated, the manual control lever causes an angular rotation of the L-shaped lever and the sliding of the guide rolls along the lateral guide slots, exerting an axial force on the thrust member having an application point which moves along the guide slots, in relation to the angular position of the L-shaped connecting lever of the device.
However, said operative connection means between the control lever and the clamping arm present a number of drawbacks; in particular, since the application point of the axial thrust exerted by the L-shaped lever is laterally spaced from the longitudinal axis of the thrust member, bending moments may arise.
This gives rise to additional overstress and frictional forces with consequent greater resistance and greater wear on the movable members of the clamping device.
Another drawback concerns the fact that, in order to rotate the clamping arm by a certain degree, the control lever must be rotated by a greater angle; in this way, actuation is made less immediate and, under certain conditions of use the rotation of the control lever may be hindered or made difficult by external obstructions.
A further drawback is related to the inevitable existence of clearances and frictional forces between the rolls of the L-shaped lever and the guide slots of the thrust member, which make it problematic to accurately determine the clamping force and the lacking conditions of the work pieces.
Another example of clamping device provided with a manually operable control lever is described in DE 196 45 778, in which the manual control lever is coaxially pivoted inside a bush which constitutes the hinging axis for the clamping arm to the box-shaped body of the device.
The operative connection between the clamping arm and the manual control lever is achieved by a side pin protruding from the pivotal axis of the control lever; said pin, during the clamping movement of the device, acts upon a connecting link of a toggle-lever mechanism, whilst when the clamping device is moved in the open condition, the pin acts upon a fork member of the rod of a linear actuator.
A device of this kind, however, presents again a number of drawbacks in that the pin presents a considerable clearance when passing from the clamping to the opening condition, thereby jeopardising the device.
In addition, since said pin is acting directly on the connecting link and on the fork member of the piston rod of the actuator, it generates considerable frictional forces, which give rise again to wear as well as to difficulty in operating the clamping device.
Moreover, said linkage system does not provide any irreversibility of the clamping arm movement in the clamped condition, since no means are provided for preventing an imperfect alignment of the links; consequently clearances and working tolerances may cause a backward rotation of the clamping arm.
In substitution of the manually operable control lever, in DE 297 01 730 a pneumatic control cylinder is provided laterally and connected to-a side of a linkage by an intermediate connecting link.
The lateral disposition of the control cylinder, as well as the disposition and conformation of the links do not allow combination both of the control lever and the control cylinder as an integrated control system in a clamping device; moreover, there is a little likelihood that a linkage system of this kind, can be adapted for use with other types of clamping devices.
A further example of a clamping device with a manual control lever is described in DE 297 01 730, which comprises a box-shaped body to which a clamping arm is pivotally supported and operatively connected to a manual control lever by a linkage or a set of links having an articulation joint movable along a linear guide path.
Since in the clamped condition of the device some links of the assembly are axially aligned with each other, the existing clearances between the links prevent a stable and precise positioning of the clamping arm. This is due to the impossibility, at the end of the closing movement, with the links in an aligned condition, to exert an additional thrust or cause a further movement of the clamping arm, necessary for compensation of the aforesaid clearances and to assume, by the same clamping arm, an unpredictable position with respect to the supporting structure.
There are also known centring devices, comprising an axially movable pin, designed to engage in appropriate holes in the work pieces, and hooking devices having one or more hook members to block one or more workpieces against a supporting structure, if necessary engaging in appropriate holes in the same work pieces. A hooking device of this kind, in combination with a centring member, is for example known from DE 201 00 701, in which a manual control rod is coaxially arranged to a linear actuator; the latter is operatively connected to the hook members by cam means which again do not ensure the irreversibility of the clamping of the work pieces in the event of external thrusts.
Therefore under particular conditions of use, manual operation by an operator, may also prove necessary for the centring and clamping devices, separately or in combination with a control actuator in an integrated working form.
The main scope of this invention is to provide a device for clamping or centring work pieces of the aforementioned types, which can be easily manually and automatically operated, while at the same time assuring a high clamping force, or an appropriate centring action precisely determined due to the elimination of clearances and frictional forces in the operative connection between the clamping member and a manual control lever of the device.
A further scope of this invention is to provide a device of the aforesaid types which is structurally simple and of such kind as to require a limited rotation of the control lever compared to the movement performed by the centring or clamping member, thereby considerably reducing the overall dimension problems, and at the same time achieving an easier operation of the same device.
A still further scope of this invention is to provide a manually operable device of the aforementioned types, which is capable of ensuring the irreversibility of the movement of the clamping member in the clamping condition of the device.
According to a first aspect of the invention a clamping device for clamping work pieces has been provided, the device comprising:
a box-shaped body having a longitudinal axis;
a clamping member movably supported by the box-shaped body between a first or forward, and a second or rearward operative positions corresponding respectively to an open and a clamped condition of the device;
a manually operable control lever pivotally supported by the box-shaped body; and
connecting means for operative connection between the clamping member and the control lever said connecting means comprising:
a guide element movable parallely to the longitudinal axis of the body;
a first toggle-lever system between the clamping member and the control lever;
a second toggle-lever system between the guide element and the control lever, said second toggle-lever system comprising first and second link members hingedly connected each others, to the guide member and to the control lever; and
in that said first and second toggle-lever system are constructed and arranged to operate in correlation with each other, in such a way that the hinge axes of the link members of the second toggle-lever system, in a forward position of the clamping member are arranged on different reference lines forming an angle between each others; and
stop means for stopping the second toggle-lever system in the forward position of the clamping member of the clamping device.
According to a further aspect of the invention a clamping device has been provided for holding and centring work pieces, the device comprising:
a box-shaped body having a longitudinal axis;
a retaining and centring member parallely arranged to the axis of the body, said centring member being movable supported between a first or backward position and a second or forward position with respect to the box-shaped body of the device, comprising:
a manually operable control lever being pivotally supported by the box-shaped body;
a guide element for the centring member; and
connecting means between the guide element and the control lever, said connecting means comprising a toggle-lever system having link members hingedly connected to the guide member and the control lever, the hinge axis of the link members being arranged on different reference lines forming an angle between each others; and
stop means being provided for stopping the toggle-lever system in the forward position of the centring member of the device.